Methods, systems, and devices for command block management are described. A memory device may receive a command (e.g., from a host device). The memory device may determine whether the command is defined by determining if the command is included within a set of defined commands. In the case that a received command is absent from the set of defined commands (e.g., the command is undefined), the memory device may block the command from being decoded for execution by the memory device. In some cases, the memory device may switch from a first operation mode to a second operation mode based on receiving an undefined command. The second operation mode may restrict an operation of the memory device, while the first mode may be less restrictive, in some cases. Additionally or alternatively, the memory device may indicate the undefined command to another device (e.g., the host device).